Conceding that 'Freewill' is a poorly defined concept, there is still some sense that we are free to make some choices and not so free to make others. Most would agree that we are free to choose vanilla vs. chocolate ice cream, while we are not free to choose to be invisible. Which is to say that some things appear to be impossilbe, regardless of what we wish them to be. While in other cases we are in some sense 'free' to make a choice.
But consider the apparent choice of ice cream flavor. Walk into a shop and look at all the options. What actually happens in your head when you make a choice? WIth various degress of concious calculation, we run through what we want. I've had vanilla before and I like it. Butter pecan I hate, and while I like chocolate I get a reaction. I've never had toffee, but people tell me it is good and I'm a bit bored so perhaps I'll try that.
In short, we calculate our choice based on past experience. This requires both data (i.e. the past experience) and an ability to calculate, however rudimentary. Sometimes the calculation is very basic: hungry. Must eat. Other times more complicated: I love chocolate ice cream, but I'll pass bacause of my weight and high blood pressure. But there is always some calculation.
What we can not change about the calculation process is this: what do I like? I submit that you are not free (in any sense) to choose to like (or not like) vanilla. Either you do, you don't, or you don't know.
Try it on yourself. Pick something you like and tell yourself that you don't like it. It can't be done.
Of course, tastes can and do change. Children tend to like more plain food than adults. Wine is famous for requiring a cultivated palate. It isn't that you've simply changed your mind: you've changed your experience. Some people will never learn to like vanilla no matter how many times they try it, while others think they don't like it until they try it and then the do.
This principle seems quite general. You can't simply decide to believe in god or not. You can't choose to be gay or not be gay. You either do, you don't or you don't know. Some experience may change your mind, but it isn't a question of freewill or choice in any sense.
Try this experiment with any idea you feel strongly about: find a friend who holds the opposite opinion and challenge them to simply change their mind in order to prove they really have freewill. It may be something with few social consequences, like ice cream, or something with more controversial, like abortion. Peel away the layers of why they believe what they believe and ultimatly you will find some atomic idea that they simply like and have absolutely no ability to change.
We appear to be determined by things we have no choice over whatever: you like this (and not that) simply because you are constructed the way you are and have experienced the things you have experienced.